Method of operating vapor generators



8- R. D. JUNKINS I 2,170,351

METHOD OF OPERATING VAPOR GENERATORS Filed July 10, 1956 2 SheetseShe-et1 Sa-mwarae FIG.1 a m f INVENTOR Au 22, 1939. R. D. JUNKINS 2,170,351

METHOD OF OPERATING VAPOR GENERATORS Filed July 10, 1936 2 Sheets-Sheet2 76 Mars Eamon/25E SUPEBHEA FEE Patented Aug. 22, 1939 men or ornnn'rmevaron eunnna'rons Raymond J assigrior to tion of Delaware T OFFICE ls,@leveland Heights, (lliio, Bailey Meter tlonipany, a corpora-Application July it, 19%, Serial No. M916 5 out,

This invention relates to the operation of heat exchangers andparticularly of evaporators. and vapor generators having small liquidstorage and a high rate of evaporation. In vapor generators 5: there isalways the problem of taking care of the solids carried by the feedliquid, unless condensate is used or extensive and expensive means areadapted to treat the feed liquid to precipitate the solids prior to theentrance of the liquid into the boiler, or the provision of treatmentsuch that the solids will be carried in suspension to a collectionchamber within the boiler, rather than allowing the solids to collect onthe interior of the tubes with consequent hard scale formation andblistering.

Prior boiler designs having large liquid storage and operating at arelatively low pressure, temperature, and rate of evaporation wereprovided with one or more mud drums, or chambers,

wherein solids could drop out of suspension or solution, due to therelative quiescence oi the liquid at that zone. Even with suchconstruction it was necessary to periodically blow down the boiler toremove the sludge, and such blowdown while serving the purpose ofkeeping the concentration of the boiler water below a predeterminedmaximum, at the same time resulted in a material loss of fluid and ofthe heat which had been put into it. In certain constructions the boilerblowdown is passed through heat exchangers for recovery of the heatwhich had been put into the liquid, but such equipment entails amaterial capital investment.

With the modem vapor generator having small 85 liquid storage and a highrate of evaporation,

there is relatively no quiescent zone wherein solids in suspension maydropout of the liquid, and

furthermore the vaporization zone wherein the vapor leaves the liquidbody is not of material cross-section such as in a drum, but may bedirectly in the tubes of sectional area. It is known that in such con.-

struction and operation the greatest concentration of solids in theliquid and the greatest tendency for accumulation of sludge and scaleupon the interior of the tube surfaces is at the vaporization zone andusually this is in a location relative to the heating such that a hightemperature is experienced. Such a combination of precipitation ofsolids on a relatively small area in highly concentrated form andsubjected to high temperature results in the formation 0! hard scalewith either a. restriction to flow within the tube passages or ablistering and burning of the tubes.

Such difllculties are particularly prevalent in relatively minute cross(till. Mb-d) the drumless forced flow type of vapor generator having afluid flow path long small bore tubes, path is initiated by includingone or more in which the flow in the the entrance of liquid underpressure at one end, and the exit of vapor only at the other end.

Such a vapor generator having small liquid storage and operated withwide range combustion devic ing practical extremely high es forms acombination renderheat release rates with the consequent ability toeconomically handle practically instantaneous load changes from minimumtomaximum, and vice versa,

without heavy standby expense, and is particularly suitable foroperating conditions suchas locomotive service, where load variationsare of a wide range and are required to be met substantiallyinstantaneously. Such a vapor generator capable of vaporizing enormousquantities of liquid and having a very small liquid stor theconcentration age capacity quickly builds up of solids, or impurities,in the stored liquid unless provision is made for periodically orcontinuously discharging a part of the highly concentrated liquid, andthus reducing the concentration of the necessity of losing liquid. Hereagain arises the heat within the blOWn the has a heat absorbing workingmedium small bore tubes with surface or flow path for the comprised ofone or more long an enlargement, preferably atthe end of the generatingsection, which acts as a separator to divide liquid and vapor;

The vapor is then while the excess liquid,

passed through a superheater 35 carried through the tubes for thepurpose of wetness and preventing scale deposit, is diverted out of theseparator under regulated conditl boiler may be operated with, forexample, to ten per cent greater Such a separator type of five 40 liquidinflow than vapor outflow, the excess water providing for tube wetnessand to carry into the separator. all of the scale forming materialswhich would otherwise continuously increase liquid body within the Thisexcess of concentration of how path. liquid, carrying a considerablesludge or scale forming materials, passing continuously into theseparator may be blown down continuously or under regulated 5 manner, asis the concentrated liquid .of the of wastin of boiler. However, hereagain the heat in such blowdown liquid, or providing heat exchangeapparatus, is encountered.

the concentration of the 45 I It has been proposed that the spilloverfrom such a separator drum be allowed to continually pass to waste.Another proposal is that such spillover be in small proportioncontinuously bled to waste and the remainder introduced at the entranceto the flow passage and thus recirculated. Such an arrangement providesfor a gradual building up of concentration within the flow path unless amaterial percentage is continuously bled to waste. The advantage lies inthe fact that the generating surface will be continuously Wetted so thateven though there is some scale deposit it will not be allowed to bake,as would be the case were the interior of the tube subjected torelatively dry vapor rather than the wetting liquid. However, the liquidwithin the flow path would continue to build up as to concentrationvalue.

A further proposal has been that the recirculated liquid be reintroducedat some intermediate point in the flow passage, but here again theconcentration in a certain section of the flow path will continuouslyincrease unless a material portion (percentage of the vapor outflow) isallowed to continuously go to waste.

A still further proposal has been that heat exchange apparatus beintroduced to reclaim the heat of all of the spillover sent to waste.This is, of course, similar in principle regardless of the type of vaporgenerator or evaporator.

By the present invention I provide that, regardless of the type of vaporgenerator, the blowdown liquid containing a maximum concentration beevaporated completely in a separate evaporator, or as in the case of theforced flow vapor generator be evaporated to dryness in a separateheated flow path which may be so located and so constructed as to bereadily cleaned or replaced.

Additionally the invention, regardless of the type of vapor generator,contemplates a continuous diversion of highly concentrated liquid, orblowdown, regulated in amount from certain variables in the boileroperation, such for example as the rate of vapor outflow demand upon thegenerator, and additionally dependent upon a measure of theconcentration or conductivity of the liquid in a certain location of thevapor generator, such for example as the vaporization drum or mud drumof a large storage boiler, or the separator of a once-through forcedcirculation boiler.

While I am aware that apparatus has been developed and utilized fordetermining the concentration and conductivity of boiler water, that theblowdown has been controlled from a measure of the conductivity of theboiler water, and furthermore in accordance with the rate of liquidinflow to the vapor generator, there has never, so far as I have beenable to determine, been proposed a method of operation wherein theactual demand upon the vapor generator as indicated by the rate of vaporoutflow is utilized either alone or in conjunction with a determinationof conductivity to control the rate of divergence of highly concentratedliquid from the vapor generator regardless of whether such liquid ispassed to waste directly, through heat exchangers, or as in accordancewith the present invention, through a separate evaporator or evaporatingsection within the vapor generator.

A principal object of the present invention is to provide that all ofthe blowdown from any type of evaporator or vapor generator be passedthrough an evaporator or evaporating section and evaporated to drynessor to substantial dryness.

Another object is that such an evaporator or evaporating section be soconstructed and located that it may readily be removed, cleaned, orreplaced.

A still further object is to provide for the removal of solids from avapor generator without loss of the heat contained in the carrierliquid.

A still further object is that in accordance with the present invention,and referring particularly to a forced flow type of vapor generator, agreater excess of liquid may be admitted relative to the vapor outflowfor the purpose of tube wetness and the carrying through of scaleforming materials without a consequent heat loss.

Another object is the provision of a control system wherein the amountof diverted liquid from the flow path or blowdown from an evaporator iscontrolled either alone'from a measure of demand upon the generator, orin combination with an indication of conductivity, or of theconcentration of the liquid.

I have chosen to illustrate and will describe my invention in connectionwith various types of vapor generators adapted to produce steam fromwater and showing the adaptability of the invention to vapor generatorswhich may have a large liquid storage space with a. relatively lowoperating pressure, temperature, and rate of evaporation, as well as inconnection with vapor generators having a very small liquid storagespace and a very high rate of evaporation.

In the drawings:

Fig. 1 diagrammatically illustrates a drumless forced flow vaporgenerator to which the present invention is directed.

Fig. 2 illustrates in diagrammatic fashion a further embodiment of myinvention.

In the drawings identical parts bear the same reference numerals.

The drumless forced flow vapor generator to which the present inventionis directed is diagrammatically illustrated in Fig. 1 to illustrate thefluid flow path as a single sinuous tube, to the economizer section I ofwhich liquid is supplied under pressure through a conduit 2 from anysource (not shown) under the control of a valve 3A. From the economizersection the fluid passes to and through the generating section 4,discharging into a separator 5. From the separator, vapor passes to andthrough the superheater 6, leaving by the conduit 1 to any vaporconsuming apparatus. Products of combustion pass successively throughthe generating section, superheater and economizer, and may contact apart or all of .the separator.

A burner 8 is supplied with fuel, such as oil, through a pipe 9 and withair to support combustion through a duct III. A control 01' the supplyof the elements of combustion forms no part of the present invention.

ll represents means responsive to liquid level within the separator andconstitutes a pressure casing enclosing a mercury U-tube connectedacross the vertical elevation of the separator. A float is adapted torise and fall with the surface ,of the mercury in one leg and to thuscause a positioning of a pointer l2 relative to an index l3 to advisethe instantaneous value of liquid level within the separator, and at thesame time to position the pilot stem ll of a pilot valve I 5 effectivein positioning the valve 32.

A rate of flow meter I6 is provided for continuously determining thedemand upon the vapor generator as indicated by the rate of vaporoutflow. Such a meter is or a known type as disclosed in the patent toLedoux 1,064,748, and ,is a differential pressure responsive deviceadapted to correct for non-linear relation between differential pressureand rate of flow, to the end that angular positioning of a pointer l'lrelative to an index it is by increments directly proportional toincrements of rate of flow. I illustrate by dotted line within the flowmeter IS the outline of the internal construction wherein is a liquidsealed bell having walls of material thick ness and shaped as describedand claimed in said patent. The meter is further adapted to position apilot stem 43 relative to a pilot casing 20 for establishing a loadingpressure representative 0! rate of vapor outflow.

' Pilots l5 and 20 are of a type forming the subject matter of thepatent to Clarence Johnson, No. 2,054,464. Air under pressure issupplied to the interior of the pilot casings I5, 20 intermediate landson the stems l4, IS. A fluid pressure in definite relation to axialmovement of the stems I 4, I3 is made available at the exit of thecasings I5, 20. I indicate pipes or capillarie's for transmitting suchair loading presthe side of the pilot casings I 5, 20 an availablesupply of compressed air from any source and at a relatively low.pressure, as for example 50 lb. per square inch gage.

I illustrate a conductivity cell 23 located near the bottom ofthe'separator 5, sensitive to con- 7 ductivityof the liquid therein, andadapted to actuate a concentration meter 24. A pointer 25 is adapted toindicate, relative to an index 25, the value oi. concentration withinthe separator 5 and simultaneously to position a valve 33.

A fluid pressure representative of the instantaneous value of rate ofvapor outflow and a fluid pressure representative of the level of liquidwithin the separator 5 are separately applied to an averaging relay 2!.The latter is efl'ective to establish a fluid pressure adapted toposition the regulating valve 32. Certain features of the relay 23 aredisclosed and claimed in the patent to Paul S. Dickey No. 2,098,913.

Particular features of my invention as depicted inthis flgure relate tothe disposal bf the liquid drained from the separator 5 through the pipe2|. It is to be understood that in this type of vapor generatorapproximately 10% more liquid is admitted through the conduit 2 thanleaves the generating section 4 as vapor. The excess liquid passing withthe steam train the generating section 4 into the separator 5 builds upa pool of liquid within the separator to a predetermined liquid level.Thereafter there is a continuous bleedondrainage of liquid from theseparator through the pipe 2| and I have herein illustrated the controlof such drainage and the disposal of same.

liquid will be vaporized. The flow through the section 34 being underthe control of the regulating valve 32, in turn positioned responsive torate of vapor outflow and to liquid level within the separator 5.

The actual size and proportion of the section 34 will depend upon thetotal capacity of the vapor generator, the actual rate of flow of liquidthrough the conduit 3| under normal operation, and the location of thesection 34 within the heated gas passage. The location relative to theheating is preferably such, as is the proportion of length and size oftubing, that all of the liquid passing through the conduit 3| into thesection 34 will be vaporized and vapor only will pass through the valve35 to the separator 5. Thus under normal conditions of operation, theliquid leaving the generating section 4 and passing to the separator 5will carry with it all of the solids originally possessed by the liquidinflow, and the excess liquid and solids passing through the conduit 2|will enter the section 34 where the liquid will be vaporized, thusleaving all of the solids in the section. If, however, under certainoperating conditions there is more liquid passing through the conduit 3|than may be evaporated in the section 34, the excess liquid along withthe vapor generated will pass into the separator 5 and recirculatethrough the conduit 2! so that no dimculty will be encountered. However,as the rating on the complete unit goes up and thus the total quantity0! liquid passing through the conduit 3| increases, at the same time theheating effective upon the section 34 will increase and thus increaseits vaporizing capacity. It is thus expected that at no time will therebe any material amount of liquid passing from the section 34 to theseparator 5.

It will be observed that the section 34 primarily serves the purpose ofcollecting all of the solids in the liquidof the separator 5, conservingall of the heat of said liquid, and vaporizing all of said liquid at apressure and temperature condition such that it may co-mingle with thevapor of the separator 5 to pass to the superheater 6.

The valve 32 is under the joint control of the meters ll, l5 andtherefore is positioned responsive not only to the rate of vaporoutflow, but also to the liquid level within the separator 5.

The conductivity cell 23, so located as to measure the concentration ofthe liquid within the separator 5, produces an indication upon the index28 of the concentration and furthermore controls the positioning of aregulating valve 33. The valve 33 is so adjusted as to normally regulatethe discharge of only a very small portion of liquid from the separator5 to waste. Under ideal conditions of operation there may be no flowwhatever thr ugh the valve 33 to waste.

The vapor ng section 34 may be removed for cleaning or replacementwhether or not the generator is in operation, by closing valves 33, 35,disconnecting flanges 33, and allowing the regulating valve 33 and handvalve 42 to take care of liquid within the separator 5.

I have illustrated provisions for washing out the section 34, while thevapor generator is in operation. By closing valves 33 and 35 and openingvalves 40 and 4|, the flow of liquid from the sep' arator 5 to thesection 34' is stopped and a now of wash water is passed through thesection 34 in opposite direction to normal flow and to waste. While suchwashing or cleaning operation is being accomplished the hand valve 42may be opened to take care 01' the excess water which reaches theseparator 5.

In Fig. 2 I illustrate in diagrammatic manner an arrangement inconnection with a drumless forced flow vapor generator, wherein theliquid discharged from the separator 5 is continuously roughlyproportioned to the rate of liquid inflow throughthe conduit 2.Furthermore that such discharged liquid passes through an external separately heated evaporator of a design which may be readily cleaned.

Liquid from the separator 5 passes through a conduit 2| to one cylindercompartment 43 of a reciprocating pump 44 driven by a motor 45. Themotor is under the control of a rheostat 45, a movable contact of whichis positioned by and with the indicator I! of the vapor outflow meterl6. Thus the liquid supply pump 44 is driven in accordance with thedemand upon the vapor generator as indicated by the rate of vaporoutflow. The general arrangement is that approximately 20% more liquidis supplied through the conduit 2 than leaves the generating sectiont-as vapor. In otherwords, one of the five cylinders of the pump 44 issupplying liquid to the conduit 2, which liquid will return through theconduit 2i and the cylinder 43. The liquid pumped by the remaining fourcylinders of the pump 44 leaves the generating section 4 as vapor.

The flow of liquid through the conduit 2| from the separator 5 isfurther controlled by means of a valve 41 responsive to a float 48.

The liquid leaving the cylinder 43 passes through a conduit 49 to asuperheated vapor evaporator 50 having hairpin tubes 5| connectingbetween compartments 52, 53. superheated vapor from the conduit 1 isadmitted under the control of a valve 54 to the compartment 53 andthence through the hairpin tubes to the compartment 52 and the conduit55 through which the now relatively cooler vapor passes to the separator5.

ized thereby, the vapor leaving by the conduit 56 to the separator 5.

The heating or vaporizing capacity of the unit 50 depends to a greatextent upon the amount of superheated vapor admitted through the valve54. However, no difilculty will be encountered should the flow of suchheating vapor be too great or too little for optimum conditions. If toogreat, then the vapor entering the separator through the conduit 55 willbe somewhat hotter than the vapor and liquid in the. separator 5. If toolittle vapor is passed through the valve 54, then the vapor through theconduit 55 will be cooled and possibly even condensed to have someliquid. Neither condition will affect the operation, as the co-minglingof such fluid entering through the conduit 55 with the vapor and liquidwithin the separator 5 will be satisfactory. At the same time an excessof heat in the unit 50 will evaporate the liquid entering through theconduit 49 faster and to possibly a higher temperature, while adeficiency of heat may result in some liquid being carried over throughthe conduit 56 to the separator 5. Again no difliculty in operation willbe encountered.

The primary object will be served in that the scale forming materialwill all be carried out of the sections l and 4 of the vapor generatorby the excess liquid to the separator 5 and from there will be pumped tothe evaporator 50 where the scale forming material will be deposited.Such an evaporator is, of course, adapted for ready removal of the tubebank for cleaning. The evaporator 50 may be removed from service forclean- The liquid entering the evaporator 50 by the conduit- 49surrounds the heating tubes 5| and is vapor- While I have illustratedand described certain preferred embodiments of my invention it is, ofcourse, understood that there may be other modes and apparatus forcarrying out the invention and that I am to be limited only as to theclaims in view of prior art.

In general, the blowdown from any evaporator or container wherein aliquid may increase in concentration, is passed to a separate evaporatorsection where the said liquid is preferably evaporated to dryness, thusdropping out the solids or scale producing material in a location whichmay be readily replaced or cleaned. Furthermore, I employ a measure ofconductivity to determine the concentration and control the blowdowntherefrom.

Certain features of my invention, described and illustrated but notclaimed herein, are disclosed and claimed in my copending divisionalapplication Serial No. 280,136 filed in the United States Patent OfliceJune 20, 1939.

What I claim as new, and desire to secure by Letters Patent of theUnited States, is:

1. The method of operating a vapor generator which includes passingvaporizable liquid through an economizer and vapor generating sectionsin excess of the vapor generated from the liquid in said sections,separating the excess liquid from the vapor in a separator, passing thevapor so separated through a superheater, and vaporizing the excessliquid in an auxiliary vapor generating section.

2. The method of operating a vapor generator which includes passingvaporizable liquid through an economizer and vapor generating sectionsin excess of the vapor generated from the liquid in said sections,separating the excess liquid from the vapor in a separator, passing thevapor so separated through a superheater, vaporizing the excess liquidin an auxiliary vapor gererating section, and returning the vaporgenerated in the auxiliary vapor generating section to the separator.

3. The method of operating a vapor generator of the forced flow typewhich includes, passing the liquid through an economizer and vaporgenerating sections, supplying liquid to the economizer and vaporgenerator sections in excess of the amount of vapor generated so thatsolids are carried inthe excess liquid and deposition of solids in theeconomizer and vapor generating sections is prevented, separating theexcess liquid from the vapor in a separator, passing the vapor soseparated through a superheater, vaporizing the excess liquid in anauxiliary vaporizing section so that the solids carried by the liquidwill be deposited therein, and'returning the vapor generated in theauxiliary vaporizing section to the separator.

4. The method of operating a vapor generator of the forced flow typehaving an economizer section, a main vapor generating section, asuperheating section, a liquid vapor separator between the vaporgenerating section and the superheating section, and an auxiliary vaporgenerating section'which includes, eflecting vaporization of less thanall of the liquid which passes through the economizer and maingenerating section to prevent the deposition of solids therein,separating the vapor from the liquid in the separator,

passing the vapor so separated through the super.-

heating section, passing the liquid separated in the separator throughthe auxiliary vapor generating section, effecting complete vaporizationof the liquid in the auxiliary vapor generating section so that solidswill be deposited therein and returning the vapor generated in theauxiliary vapor generating section to the separator.

5. The method of operatinga vapor generator having an economizersection, a vapor generating section, a superheating section, and aliquid-vapor separator between the vapor generating and superheatingsections'which includes, heating the vapor, generator so that more than50% and less than 90% of the liquid'admitted to the economizer sectionis vaporized in the economizer and vapor generating sections, eiifectingseparation of the liquid and vapor in the separator, passing the vaporthrough the superheating section, diverting the liquid separated fromthe vapor in the separator through an auxiliary vapor generating sectionso that substantially all of the liquid is vaporized, and returning thevapor so formed in the auxiliary vaporizing section to the vaporseparator.

RAYMOND D. JUNKINS.

